As for the production of tetrachloroethylene (CCl2═CCl2) (hereinafter sometimes referred to as “PCE”), for example, (1) a method of thermally decomposing carbon tetrachloride, (2) a method of simultaneously conducting chlorination and dehydrochlorination of a chloroolefin, and (3) a method of using chlorine and a hydrocarbon such as natural gas or LPG as starting materials are known. In the methods, a stabilizer is added so as to ensure the stability of tetrachloroethylene and, in general, the stabilizer is added in an amount of hundreds to thousands of ppm. As for uses, tetrachloroethylene is used, for example, as a dry cleaning solvent, a starting material for the production of a fluorocarbon gas, or a solvent.
On the other hand, as for the production of pentafluoroethane (CF3CHF2), for example, (1) a method of fluorinating tetrachloroethylene or a fluorinated product thereof with hydrogen fluoride (see, Japanese International Application Domestic Publication No. 9-511515, etc.), (2) a method of hydrogenolyzing chloropentafluoroethane (CClF2CF3) (see, Japanese Unexamined Patent Publication No. 5-97728 (JP-A-5-97728), etc.) and (3) a method of reacting a fluorine gas with halogen-containing ethylene (see, Japanese Unexamined Patent Publication No. 1-38034 (JP-A-1-38034)) are known.
For example, in the method of producing pentafluoroethane by reacting tetrachloroethylene with hydrogen fluoride in a gas phase in the presence of a fluorination catalyst, the reaction is conducted through two steps different in reaction conditions. More specifically, this method comprises a first reaction where tetrachloroethylene and hydrogen fluoride (HF) are reacted in a gas phase in the presence of a fluorination catalyst to mainly produce 1,1-dichloro-2,2,2-trifluoroethane (CHCl2CF3) and 1-chloro-1,2,2,2-tetrafluoroethane (CHClFCF3), and a second reaction where the product mainly composed of CHCl2CF3 and CHClFCF3 produced in the first reaction is reacted with HF in a gas phase in the presence of a fluorination catalyst to mainly produce pentafluoroethane.
In this method, tetrachloroethylene as one of starting materials for the first reaction contains a stabilizer usually on the order of tens to hundreds of mass ppm so as to prevent, for example, the generation of an acid content due to decomposition. For example, a hydroxyl group-containing aromatic compound, such as phenol or cresol, is contained and if such a stabilizer is not contained in tetrachloroethylene, the tetrachloroethylene lacks in stability and a side reaction such as generation of an acid content proceeds.
However, the stabilizer contained in tetrachloroethylene gives rise to deterioration of the activity of a catalyst used for the production of pentafluoroethane. Therefore, a stabilizer is preferably not contained. This may be attained, for example, by removing the stabilizer before the first reaction. However, conventional removing methods by fractional distillation or the like have a problem in that the operation is cumbersome and the equipment therefor is expensive.
Further, hydrofluorocarbons (hereinafter sometimes referred to as “HFC”) have an ozone depletion potential of 0. Among hydrofluorocarbons, pentafluoroethane (hereinafter sometimes referred to as “HFC-125”) and 1,1,1,2-tetrafluoroethane (hereinafter sometimes referred to as “HFC-134a”) are useful compounds, for example, as refrigerants.
As for the production of pentafluoroethane, for example, a method of reacting hydrogen fluoride with tetrachloroethylene, 2,2-dichloro-1,1,1-trifluoroethane (hereinafter sometimes referred to as “HCFC-123”) or 2-chloro-1,1,1,2-tetrafluoroethane (hereinafter sometimes referred to as “HCFC-124”) in the presence of a fluorination catalyst is known.
Also, a method of obtaining pentafluoroethane through two steps of reacting hydrogen fluoride with tetrachloroethylene in the presence of a fluorination catalyst to produce an intermediate product gas mainly comprising HCFC-123 and/or HCFC-124 which are intermediates of pentafluoroethane, and reacting hydrogen fluoride with the gas containing these intermediates in the presence of a fluorination catalyst to obtain pentafluoroethane, may be used. More specifically, a process of reacting hydrogen fluoride with tetrachloroethylene, shown by the following formula 1 and/or formula 2 is conducted in a first reactor to produce an intermediate product rich in intermediates HCFC-123 and/or HCFC-124, and respective intermediates are reacted with hydrogen fluoride in a second reactor as shown by the following formula 3 and/or formula 4, whereby a product containing the objective pentafluoroethane is obtained.CCl2=CCl2+3HF→CF3CHCl2+2HCl  (Formula 1)CCl2=CCl2+4HF→CF3CHClF+3HCl  (Formula 2)CF3CHCl2+2HF→CF3CHF2+2HCl  (Formula 3)CF3CHClF+HF→CF3CHF2+HCl  (Formula 4)
As for the production of 1,1,1,2-tetrafluoroethane, for example, a method of reacting hydrogen fluoride with trichloroethylene or 2-chloro-1,1,1-trifluoroethane (hereinafter sometimes referred to as “HCFC-133a”) in the presence of a fluorination catalyst is known. Also, similarly to the above-described pentafluoroethane, a two-step method may be used. That is, a reaction of reacting trichloroethylene with hydrogen fluoride, shown by the following formula 5 is performed in a first reactor to produce an intermediate product rich in an intermediate HCFC-133a and subsequently, HCFC-133a is reacted with hydrogen fluoride in a second reactor as shown by formula 6, whereby a product containing objective 1,1,1,2-tetrafluoroethane is obtained.CCl2=CHCl+3HF→CF3CH2Cl+2HCl  (Formula 5)CF3CH2Cl+HF→CF3CH2F+HCl  (Formula 6)
Furthermore, a method of producing two or more hydrofluorocarbons at the same time has been proposed. For example, WO95/15937 describes a method of reacting HCFC-133a with hydrogen fluoride to produce 1,1,1,2-tetrafluoroethane and reacting hydrogen fluoride with methylene chloride and trichloroethylene in the presence of the produced 1,1,1,2-tetrafluoroethane.
Japanese International Application Domestic Publication No. 7-507787 describes a method of reacting hydrogen fluoride, for example, with trichloroethylene to produce HCFC-133a, then reacting this HCFC-133a with hydrogen fluoride to produce 1,1,1,2-tetrafluoroethane, and during these steps, adding, for example, HCFC-123 and/or HCFC-124, thereby producing pentafluoroethane together with 1,1,1,2-tetrafluoroethane.
Also, Japanese Unexamined Patent Publication No. 8-27046 (JP-A-8-27046) describes a method of reacting hydrogen fluoride, for example, with HCFC-133a and HCFC-123 in a first rector, mixing the reaction product with tetrachloroethylene, feeding the mixture to a second reactor, and conducting a reaction under reaction conditions different from those in the first reactor, thereby obtaining a product containing 1,1,1,2-tetrafluoroethane and pentafluoroethane.
However, these methods have a problem particularly in simultaneously producing high-purity pentafluoroethane and 1,1,1,2-tetrafluoroethane in an economically advantageous manner using tetrachloroethylene and trichloroethylene which are general-purpose raw materials.
The reason therefor is that the reaction conditions in respective reactions shown by formulae 1 to 6 greatly differ from each other. To speak specifically on preferred reaction conditions in the production of pentafluoroethane, the steps shown by formulae 1 and 2 can be conducted under the conditions of, for example, a reaction pressure of 0.35 MPa, a reaction temperature of 310° C. and a hydrogen fluoride/tetrachloroethylene molar ratio of 10. Furthermore, the steps shown by formulae 3 and 4 can be conducted under the conditions of, for example, a reaction pressure of 0.4 MPa, a reaction temperature of 340° C. and a hydrogen fluoride/HCFC-123+HCFC-124 molar ratio of 8.
To speak specifically on preferred reaction conditions in the production of 1,1,1,2-tetrafluoroethane, the step shown by formula 5 can be conducted under the conditions of, for example, a reaction pressure of 0.35 MPa, a reaction temperature of 270° C. and a hydrogen fluoride/trichloroethylene molar ratio of 15. The step shown by formula 6 can be conducted under the conditions of, for example, a reaction pressure of 0.4 MPa, a reaction temperature of 340° C. and a hydrogen fluoride/HCFC-133a molar ratio of 6.
In particular, the optimal reaction temperature greatly differs between the steps of reacting hydrogen fluoride with respective starting materials of tetrachloroethylene and trichloroethylene and therefore, if a conventional method is used, this great difference in the reaction temperature brings out adverse effect of unreacted starting materials on the catalyst or causes increase of undesired impurities in some cases.